Palladium and palladium alloys have numerous uses because of their chemical inertness, excellent wearability, bright finish, high thermal and electrical conductivity and low cost as compared to gold. Many such applications involve electrical contact surfaces such as connector pins, relay or switch contacts, contact surfaces on printed wiring boards, as well as costume jewelry. For many of such applications large amounts of palladium are plated very rapidly exhausting palladium content of the bath and replenishment of palladium in the bath becomes highly desirable. A typical example is palladium plating of contact pins for electrical connectors where large numbers of pins are electroplated at high speeds. A number of patents issued to J. A. Abys et al. disclose palladium and palladium alloy compositions and procedures for their electroplating, including U.S. Pat. No. 4,427,502, issued on Jan. 24, 1984; U.S. Pat. No. 4,468,296, issued on Aug. 28, 1984; U.S. Pat. No. 4,486,274, issued on Dec. 4, 1984; U.S. Pat. No. 4,911,798, issued on Mar. 27, 1990; U.S. Pat. No. 4,911,799, issued on Mar. 27, 1990; and U.S. Pat. No. 4,493,754 , issued on Jan. 15, 1985, each of which is incorporated herein by reference.
Certain class of palladium compounds, generally referred to in this application as palladium ammine hydroxide compounds, are useful in palladium plating. The exact structural formula for the palladium ammine hydroxide is not known and possibly more than one species exists in aqueous solutions corresponding generally to the formula [Pd(NH.sub.3).sub.2 (OH)].sub.n (OH).sub.n where n may vary from 1 to 6. The palladium ammine hydroxide compound may be used to initially make up the palladium plating bath and/or to replenish the bath during the plating operation. The use of palladium ammine hydroxide in palladium plating baths has several advantages. For example, acidic anions, such as chloride ions, do not accumulate in the bath. Such accumulation of acidic anions often limits the lifetime of the bath and sometimes alters the plating characteristics of the bath during the lifetime of the bath. Also, palladium ammine hydroxide compounds neutralize hydrogen ions produced at the anode so that alkaline agents (e.g., potassium hydroxide) need not be added to the bath thus reducing accumulation of alkaline cations (e.g., potassium ions in the case of potassium hydroxide) which limit the usefulness and lifetime of the bath. Further, a constant palladium concentration being maintained by addition of palladium ammine hydroxide compound during the plating insures stability of pH for the plating bath. In turn, this leads to longer bath lifetimes and more constant plating conditions (plating rate, etc.) throughout the lifetime of the bath.
A procedure for synthesizing palladium ammine hydroxide for use in palladium plating baths is disclosed in U.S. Pat. No. 4,512,963, issued on Apr. 23, 1988 to J. A. Abys et al. This patent discloses a process for producing palladium ammine hydroxide using an anion exchange resin (OH-form). Unfortunately, this process is slow and expensive because the exchange resin is not readily reusable and recovery of the hydroxide from the resin is tedious and incomplete. Therefore, there is a need for a procedure for producing palladium ammine hydroxide in a simple and efficient manner in a form readily usable in the palladium bath and having a relatively long shelf lifetime.